[pushed] Fix ptid_t selftest crash

[Tom Tromey <tromey@adacore.com>]

Sam James pointed out that my recent patch to add ptid_t::parse caused
a selftest crash.

At first I couldn't see why this did not crash for me, but then I
realized that ptid_t::parse didn't unconditionally initialize '*obuf'.
Initializing it to nullptr made this crash reliably.

The underlying bug is that some code paths in ptid_t::parse don't set
obuf on return.  This patch fixes the bug by passing 'obuf' down to
hex_or_minus_one.

Since this is straightforward and fixes a new crash, I'm checking it
in.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=34340
---
 gdb/unittests/ptid-selftests.c | 2 +-
 gdbsupport/ptid.cc             | 5 +----
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/gdb/unittests/ptid-selftests.c b/gdb/unittests/ptid-selftests.c
index c02401db952..b52c98cdc54 100644
--- a/gdb/unittests/ptid-selftests.c
+++ b/gdb/unittests/ptid-selftests.c
@@ -154,7 +154,7 @@ static_assert (!ptid_t (2, 2, 2).matches (both),
 static ptid_t
 parse_one (const char *str, bool for_remote)
 {
-  const char *out;
+  const char *out = nullptr;
   ptid_t result = ptid_t::parse (str, &out, for_remote,
     [] ()
       {
diff --git a/gdbsupport/ptid.cc b/gdbsupport/ptid.cc
index 731a5bc3da3..5de1da3ba44 100644
--- a/gdbsupport/ptid.cc
+++ b/gdbsupport/ptid.cc
@@ -119,7 +119,7 @@ ptid_t::parse (const char *buf, const char **obuf, bool for_remote,
     }
 
   /* No multi-process.  Just a thread id.  */
-  hex = hex_or_minus_one (p, &pp, for_remote);
+  hex = hex_or_minus_one (p, obuf, for_remote);
 
   /* Handle special thread ids.  */
   if (hex == (ULONGEST) -1)
@@ -134,8 +134,5 @@ ptid_t::parse (const char *buf, const char **obuf, bool for_remote,
 
   pid = default_pid ();
 
-  if (obuf != nullptr)
-    *obuf = pp;
-
   return ptid_t (pid, lwp);
 }

base-commit: c2d4b5e1135f75f7e4ef7ff68fa899bfe483671b
-- 
2.54.0